Sodium hydrogen bis­(phenoxy­acetate)

In the title compound, Na⁺·H⁺·2C₈H₇O₃⁻, the anion contains a short Speakman-type hydrogen bond [O...O = 2.413 (2) Å]. The anions and the Na atoms lie across twofold axes.

S1. Comment

The structure of the title compound, (I), was determined during an investigation into the effect of impurities on the crystallization and intermolecular interactions of phenoxyacetic acid. Anhydrous sodium phenoxyacetate (NaPAA) was crystallized from tap water to mimic the industrial manufacturing process undergoing investigation. The ratio of sodium to phenoxyacetate ions in (I) is 1:2 so an acidic hydrogen atom is required to balance the charges. H22 was located on a twofold axis between two carboxy oxygen atoms O22···O22ⁱ (i = 1 - x, y, 5/2 - z) which are 2.413 (2) Å apart. This hydrogen bond is very short but precedented (Freyhardt et al., 2000; Speakman & Muir, 1982; Speakman et al., 1981). This link is another strand which weaves around the inner ionic Na—O—Na core. H22 makes another, longer bond with O21. This carboxylate O atom has close contacts with sodium ions whereas the other O atom, O22, has a closer contact with H22 [1.215 (5) Å]. \sch

The polymeric core of (I) consists of a carboxylate oxygen atom (O21) bridging sodium atoms forming a twisted ribbon, where the two Na-µ-O—Na planes are inclined at 48.5° to each other. These ribbons lie parallel to the crystallographic c axis. The sodium co-ordination sphere consists of four Na—O21 contacts: two of 2.3385 (15) and two of 2.3815 (14) Å from four phenoxyacetic acid molecules. The latter two molecules with the longer Na—O21 contacts also bond to sodium via the phenoxy O atom, O1, where the Na—O1 distance is 2.6102 (15) Å. This packing arrangement is significantly different from that in sodium phenoxyacetate hemihydrate (Prout et al., 1971), where the sodium ion is surrounded by oxygen atoms from one water and two phenoxyacetate molecules. The NaO core of (I) is surrounded on either side by the phenoxy groups which form hydrocarbon layers above and below the ionic core.

The carboxylate group is almost coplanar with the phenyl ring (angle between the planes containing COO and Ph groups, 8.2°) and several structural trends were identified in the carboxylate chain. Firstly, distortion of exo-O1 angles where both C15—C10—O1 and C11—C10—O1 [123.3 (18) and 116.34 (17)°, respectively] deviate from the trigonal angle (120°). The distortion is thought to arise from the steric requirements of the carboxylate side chain, which is well documented among the phenoxyalkanoic series (Kennard et al., 1982). The distances of 1.273 (2) and 1.235 (2) Å (C21—O22, C21—O21) and the angles, 111.75 (16) and 121.59 (17)° (O22—C21—C20 and O21—C21—C20, respectively) are similar to those seen in the hemi-hydrate [1.276 (10), 1.240 (10) Å, 114.2 (7) and 117.5 (7)°] (Prout et al., 1971). In phenoxyacetic acid, the similar C═O and C—OH distances [1.266 (3) and 1.263 (3) Å] are considered to originate from disorder of the acidic proton (Kennard et al., 1982).

Related literature

For related literature, see: Freyhardt et al. (2000); Kennard et al. (1982); Prout et al. (1971); Speakman & Muir (1982); Speakman et al. (1981).

S2. Experimental

A sample of powdered sodium phenoxyacetate hemihydrate (Sigma-Aldrich) was dissolved in Edinburgh tap water, and single crystals of (I) were obtained by slow evaporation.

S3. Refinement

The hydrogen atom H22 was located in the difference map and coordinates were freely refined. Other H atoms were treated as riding with C—H 0.95–099 Å.

Computing details

Data collection: XSCANS (Bruker, 1996); cell refinement: XSCANS; data reduction: SHELXTL (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The asymmtric unit of (I): atoms H22 and Na lie on twofold rotation axes. Displacement ellipsoids are shown at the 50% probability level.
	Fig. 2. Packing arrangement viewed down the b axis. Oxygen atoms are cross-hatched and sodium atoms have a diagonal stripe.

Sodium hydrogenbis(phenoxyacetate)

Crystal data

[Na(C8H7O3)2H]	F(000) = 676
Mr = 326.27	Dx = 1.454 Mg m^−3
Orthorhombic, Pbcn	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2n 2ab	Cell parameters from 39 reflections
a = 21.484 (3) Å	θ = 1.9–17.5°
b = 9.4624 (8) Å	µ = 0.14 mm^−1
c = 7.3293 (7) Å	T = 160 K
V = 1490.0 (3) Å^3	Plate, colourless
Z = 4	0.58 × 0.34 × 0.06 mm

Data collection

Bruker P4 diffractometer	1020 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.036
Graphite monochromator	θmax = 25.0°, θmin = 1.9°
ω scans	h = −1→25
Absorption correction: ψ scan (North et al., 1968)	k = −11→1
Tmin = 0.966, Tmax = 0.992	l = −1→8
1814 measured reflections	3 standard reflections every 97 reflections
1312 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.039	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.109	H atoms treated by a mixture of independent and constrained refinement
S = 0.96	w = 1/[σ^2(Fo^2) + (0.0636P)^2 + 0.2133P] where P = (Fo^2 + 2Fc^2)/3
1311 reflections	(Δ/σ)max < 0.001
107 parameters	Δρmax = 0.17 e Å^−3
0 restraints	Δρmin = −0.23 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Na1	0.5000	0.02051 (11)	0.7500	0.0223 (3)
O1	0.41147 (6)	0.20753 (15)	0.71555 (19)	0.0242 (4)
O21	0.47164 (6)	0.14081 (14)	1.02304 (18)	0.0225 (4)
O22	0.46179 (8)	0.36168 (14)	1.1294 (2)	0.0337 (4)
C10	0.37299 (9)	0.2366 (2)	0.5683 (3)	0.0207 (5)
C11	0.36417 (9)	0.1277 (2)	0.4444 (3)	0.0240 (5)
H11A	0.3852	0.0403	0.4603	0.029*
C12	0.32447 (10)	0.1471 (2)	0.2973 (3)	0.0275 (5)
H12A	0.3184	0.0725	0.2125	0.033*
C13	0.29347 (10)	0.2749 (2)	0.2728 (3)	0.0292 (5)
H13A	0.2660	0.2877	0.1727	0.035*
C14	0.30341 (9)	0.3829 (2)	0.3967 (3)	0.0264 (5)
H14A	0.2822	0.4702	0.3814	0.032*
C15	0.34372 (9)	0.3661 (2)	0.5428 (3)	0.0228 (5)
H15A	0.3512	0.4422	0.6244	0.027*
C20	0.41523 (10)	0.3152 (2)	0.8520 (3)	0.0243 (5)
H20A	0.3728	0.3405	0.8936	0.029*
H20B	0.4347	0.4008	0.7996	0.029*
C21	0.45322 (10)	0.2641 (2)	1.0125 (3)	0.0210 (5)
H22	0.5000	0.346 (4)	1.2500	0.076 (15)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Na1	0.0320 (6)	0.0178 (5)	0.0171 (5)	0.000	−0.0012 (5)	0.000
O1	0.0312 (8)	0.0220 (7)	0.0193 (7)	0.0073 (6)	−0.0064 (6)	−0.0026 (6)
O21	0.0302 (8)	0.0175 (7)	0.0199 (7)	0.0042 (6)	−0.0013 (6)	0.0012 (6)
O22	0.0527 (10)	0.0201 (7)	0.0283 (9)	0.0085 (7)	−0.0168 (8)	−0.0052 (7)
C10	0.0204 (9)	0.0244 (10)	0.0174 (10)	−0.0007 (8)	0.0004 (8)	0.0032 (9)
C11	0.0265 (11)	0.0215 (10)	0.0242 (10)	0.0003 (8)	0.0033 (9)	0.0009 (9)
C12	0.0279 (11)	0.0321 (11)	0.0224 (11)	−0.0066 (9)	−0.0003 (9)	−0.0027 (9)
C13	0.0234 (9)	0.0393 (12)	0.0250 (11)	−0.0056 (10)	−0.0052 (9)	0.0070 (10)
C14	0.0236 (10)	0.0271 (11)	0.0285 (11)	0.0002 (9)	−0.0013 (9)	0.0076 (9)
C15	0.0249 (10)	0.0222 (10)	0.0214 (10)	0.0002 (9)	0.0021 (9)	0.0015 (9)
C20	0.0338 (11)	0.0189 (10)	0.0203 (11)	0.0032 (9)	−0.0047 (9)	−0.0020 (8)
C21	0.0241 (10)	0.0193 (10)	0.0196 (10)	−0.0008 (8)	0.0024 (8)	0.0010 (8)

Geometric parameters (Å, º)

Na1—O21^i	2.3385 (15)	C10—C11	1.386 (3)
Na1—O21^ii	2.3385 (15)	C10—C15	1.390 (3)
Na1—O21	2.3815 (14)	C11—C12	1.387 (3)
Na1—O21^iii	2.3815 (14)	C11—H11A	0.9500
Na1—O1^iii	2.6102 (15)	C12—C13	1.392 (3)
Na1—O1	2.6102 (15)	C12—H12A	0.9500
Na1—Na1^iv	3.6851 (4)	C13—C14	1.384 (3)
Na1—Na1^ii	3.6851 (4)	C13—H13A	0.9500
O1—C10	1.387 (2)	C14—C15	1.386 (3)
O1—C20	1.430 (2)	C14—H14A	0.9500
O21—C21	1.235 (2)	C15—H15A	0.9500
O21—Na1^ii	2.3385 (15)	C20—C21	1.511 (3)
O22—C21	1.273 (2)	C20—H20A	0.9900
O22—H22	1.216 (6)	C20—H20B	0.9900
O21^i—Na1—O21^ii	98.50 (7)	C21—O21—Na1^ii	138.15 (13)
O21^i—Na1—O21	147.47 (7)	C21—O21—Na1	118.77 (13)
O21^ii—Na1—O21	77.34 (5)	Na1^ii—O21—Na1	102.66 (5)
O21^i—Na1—O21^iii	77.34 (5)	C21—O22—H22	119.7 (18)
O21^ii—Na1—O21^iii	147.47 (7)	C11—C10—O1	116.34 (17)
O21—Na1—O21^iii	122.89 (8)	C11—C10—C15	120.36 (19)
O21^i—Na1—O1^iii	134.52 (5)	O1—C10—C15	123.30 (18)
O21^ii—Na1—O1^iii	100.60 (5)	C10—C11—C12	119.65 (19)
O21—Na1—O1^iii	77.35 (5)	C10—C11—H11A	120.2
O21^iii—Na1—O1^iii	64.58 (5)	C12—C11—H11A	120.2
O21^i—Na1—O1	100.60 (5)	C11—C12—C13	120.6 (2)
O21^ii—Na1—O1	134.52 (5)	C11—C12—H12A	119.7
O21—Na1—O1	64.58 (5)	C13—C12—H12A	119.7
O21^iii—Na1—O1	77.35 (5)	C14—C13—C12	118.87 (19)
O1^iii—Na1—O1	94.63 (7)	C14—C13—H13A	120.6
O21^i—Na1—Na1^iv	39.09 (3)	C12—C13—H13A	120.6
O21^ii—Na1—Na1^iv	129.69 (6)	C13—C14—C15	121.24 (19)
O21—Na1—Na1^iv	152.37 (5)	C13—C14—H14A	119.4
O21^iii—Na1—Na1^iv	38.25 (3)	C15—C14—H14A	119.4
O1^iii—Na1—Na1^iv	99.65 (4)	C14—C15—C10	119.18 (19)
O1—Na1—Na1^iv	88.58 (4)	C14—C15—H15A	120.4
O21^i—Na1—Na1^ii	129.69 (6)	C10—C15—H15A	120.4
O21^ii—Na1—Na1^ii	39.09 (3)	O1—C20—C21	110.34 (15)
O21—Na1—Na1^ii	38.25 (3)	O1—C20—H20A	109.6
O21^iii—Na1—Na1^ii	152.37 (5)	C21—C20—H20A	109.6
O1^iii—Na1—Na1^ii	88.58 (4)	O1—C20—H20B	109.6
O1—Na1—Na1^ii	99.65 (4)	C21—C20—H20B	109.6
Na1^iv—Na1—Na1^ii	167.91 (6)	H20A—C20—H20B	108.1
C10—O1—C20	115.91 (14)	O21—C21—O22	126.65 (19)
C10—O1—Na1	130.08 (11)	O21—C21—C20	121.59 (17)
C20—O1—Na1	111.97 (11)	O22—C21—C20	111.75 (16)
O21^i—Na1—O1—C10	−21.89 (16)	O1^iii—Na1—O21—Na1^ii	−104.10 (6)
O21^ii—Na1—O1—C10	−135.15 (15)	O1—Na1—O21—Na1^ii	154.47 (7)
O21—Na1—O1—C10	−171.29 (16)	Na1^iv—Na1—O21—Na1^ii	169.24 (8)
O21^iii—Na1—O1—C10	52.42 (15)	C20—O1—C10—C11	−173.82 (17)
O1^iii—Na1—O1—C10	115.07 (16)	Na1—O1—C10—C11	24.0 (2)
Na1^iv—Na1—O1—C10	15.50 (15)	C20—O1—C10—C15	5.6 (3)
Na1^ii—Na1—O1—C10	−155.59 (15)	Na1—O1—C10—C15	−156.60 (14)
O21^i—Na1—O1—C20	175.33 (12)	O1—C10—C11—C12	177.60 (18)
O21^ii—Na1—O1—C20	62.06 (15)	C15—C10—C11—C12	−1.9 (3)
O21—Na1—O1—C20	25.93 (12)	C10—C11—C12—C13	0.1 (3)
O21^iii—Na1—O1—C20	−110.36 (13)	C11—C12—C13—C14	0.7 (3)
O1^iii—Na1—O1—C20	−47.72 (11)	C12—C13—C14—C15	0.4 (3)
Na1^iv—Na1—O1—C20	−147.28 (12)	C13—C14—C15—C10	−2.2 (3)
Na1^ii—Na1—O1—C20	41.63 (13)	C11—C10—C15—C14	2.9 (3)
O21^i—Na1—O21—C21	−100.17 (15)	O1—C10—C15—C14	−176.51 (18)
O21^ii—Na1—O21—C21	173.87 (17)	C10—O1—C20—C21	174.29 (16)
O21^iii—Na1—O21—C21	21.76 (13)	Na1—O1—C20—C21	−20.30 (19)
O1^iii—Na1—O21—C21	69.77 (15)	Na1^ii—O21—C21—O22	24.3 (3)
O1—Na1—O21—C21	−31.66 (14)	Na1—O21—C21—O22	−146.74 (18)
Na1^iv—Na1—O21—C21	−16.9 (2)	Na1^ii—O21—C21—C20	−154.49 (15)
Na1^ii—Na1—O21—C21	173.87 (17)	Na1—O21—C21—C20	34.5 (2)
O21^i—Na1—O21—Na1^ii	85.96 (13)	O1—C20—C21—O21	−6.6 (3)
O21^ii—Na1—O21—Na1^ii	0.0	O1—C20—C21—O22	174.50 (17)
O21^iii—Na1—O21—Na1^ii	−152.11 (6)

Symmetry codes: (i) x, −y, z−1/2; (ii) −x+1, −y, −z+2; (iii) −x+1, y, −z+3/2; (iv) −x+1, −y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O22—H22···O22^v	1.22 (1)	1.22 (1)	2.413 (2)	166 (4)

Symmetry code: (v) −x+1, y, −z+5/2.